Conventional techniques for mass producing three-dimensional objects typically include casting, deforming, machining and assembling. While such techniques are capable of producing complicated objects in high volume at relatively low cost, they are often poorly adapted for rapid prototyping, and for relatively short production runs.
Direct CAD Manufacturing systems (DCM) are somewhat better adapted to rapid prototyping. In DCM systems computers are employed to produce a three-dimensional model of a desired object, and then to drive servo-mechanisms which produce the desired object. This generally involves machining or application of other subtractive processes on a starting block of material. Subtractive DCM has proven to be cost effective in automotive, aerospace, appliance, toy manufacturing, and many other industries that involve repeated design and prototyping of parts. Such systems, however, are not well suited to producing prototypes having complicated internal construction. This is a natural function of starting the process with a substantially solid block of material, and machining the part from the outside.
Additive DCM systems address this problem by producing a three-dimensional object from a large number of individual layers. The layers can be machined in the normal fashion and then pinned, welded or otherwise held together, or they can be deposited one on top of the other through deposition of a flowable build material. The latter systems are generically referred to herein as Sold Freeform Fabrication (SFF) systems.
In SFF systems each layer is typically only about 0.1 to 0.25 mm. thick. This provides about 40 to 100 layers for each cm of object, and allows SFF systems to produce objects having complicated internal structure. While SFF systems may not have yet be able to produce objects having exactly the same shape achievable with other methods, they are generally able to produce "near net shape" objects, i.e., those having substantially the end-shape desired, and which can then be readily finished by conventional processing steps. For convenience in the descriptions herein, the term "object" is employed to mean both the final object and any intermediate near net shaped object. In a similar manner, the terms "fabricate" and "fabricating" are used herein to include both production of a final product from a starting material, and production of a recognizable intermediate. Thus, a "method for fabricating a three-dimensional object "may involve merely producing an intermediate that is visibly similar to the finished object or product, but which requires additional processing to arrive at the finished object or product.
In addition to producing fairly complicated objects, SFF systems may advantageously employ multiple deposition heads to deposit a plurality of different materials. U.S. Pat. Nos. 4,999,143 and 5,569,349 (October 1996) to Almquist et al., for example, describe depositing both a build material and a supporting material in a series of layers. Moreover, while there is little or no enablement in this area, it has also been suggested that different build materials can be employed within a single layer to produce an electrically conductive path.
In SFF systems it is generally desirable to harden or otherwise cure the flowable build material deposited at each layer according to a pattern that matches a corresponding cross-section of the object being produced. While numerous different systems and methods have been proposed, there are conceptually only two classes of methods for hardening the layers in predetermined patterns--selective deposition and selective curing. In selective deposition methods, the build material is laid down from the outset in the desired pattern, and then typically cured via cooling or polymerization. Suitable apparatus for this class of methods necessarily involves some sort of delivery dispenser that is moveable with respect to the rest of the build. Examples of such delivery dispensers are the extrusion head of U.S. Pat. No. 4,749,347 to Valavaara, and the droplet emitting head of U.S. Pat. No. 4,665,492 to Masters.
In selective curing methods, the build material is deposited across an entire surface, or throughout an entire volume, and then energy is imparted to selected portions of the build material to produce the desired pattern. At some point in the process the non-cured material is then washed or brushed away. Light energy is typically employed to produce the desired pattern, and many extant systems employ one or more laser beams to trace out the desired images in the deposited build material. Lasers have been employed in this manner for laser sintering of build materials containing a metal, a metal containing powder, or a plastic, as described in U.S. Pat. No. 4,752,352 to Feygin, U.S. Pat. No. 4,863,538 to Deckard and U.S. Pat. No. 4,938,816 to Beaman et al. It is also known to apply light energy to the deposited build material in a pattern that corresponds to an entire cross-sectional image. This method is generally referred to as sterolithography, and various embodiments are described in U.S. Pat. Nos. 4,929,402 and 5,236,637 to Hull, and U.S. Pat.
Nos. 4,961,154 and 5,031,230 to Pomerantz et al.
In the last several years advances in SFF systems have driven a demand to provide functional properties in SFF produced objects that are comparable to those of conventionally produced objects. Among other things, manufacturers have expressed a desire to provide SFF produced objects that have the strength and crack resistance approaching that of forged metal components. A desire has also been expressed to provide SFF objects that include conducting paths, such as electrical, thermal or magnetic conduction paths.
Sinterable metals, alloys and ceramics can be used to produce final products having excellent structural strength, (see e.g., U.S. Pat. No. 5,496,892 to Quadir et al., and U.S. Pat. No. 4,906,424 to Hughes et al.). But these materials are generally unsuitable as build materials in SFF systems because they become fluid only at high temperatures or pressures. This creates considerable difficulties in handling and deposition, among other things by limiting the rate at which new layers can be applied to a build. The problem can be resolved to some extent by ejecting small particles or droplets from a dispenser rather than extruding relatively larger masses, but operating conditions are still severe, and generally unsuited for many applications. The problem can be resolved somewhat further by using an electrorheological support during the deposition process, as taught in U.S. Pat. No. 5,362,427 to Mitchell (November 1994), but that solution adds yet additional complications. In any event, the extreme deposition conditions presently required for depositing metal and alloy build materials in SFF systems largely preclude the inclusion of plastics or other materials during the build process, which all but eliminates the inclusion of many desirable functional properties in SFF products.
Metal containing powders such as aluminum oxide, zirconium silicate, fused silica, and silicon carbide are relatively easy to deposit, such as by the slurry droplet method of U.S. Pat. No. 4,665,492 to Masters (May 1987), but are difficult to bind together to provide adequate strength. Among other things cracking is a serious problem. Low temperature sintering can be used to ameliorate this problem to some extent, but requires inordinate amounts of time. High temperature sintering can also be used, but requires difficult or adverse conditions, and is only moderately effective. Binders can also be used to increase inter-particle strength, as described in U.S. Pat. No. 5,660,621 to Bredt (August 1997), but SFF processes using extant binders still tend to provide only relatively weak structures.
Polymerizable build materials are easier to handle and deposit, but generally provide poor structural strength. Such materials are also not known to provide the many functional qualities that may be desired. In addition, the form energy used to initiate polymerization may itself be problematic. Many photopolymers, for example, utilize UV radiation which can cause injury. Still further, the time required for the photopolymers to solidify upon exposure to UV radiation can be prohibitively long, thereby inordinately increasing the build time.
Waxes, thermosetting and thermoplastic materials, two-part epoxies, foaming plastics, and glass have also all been used in conjunction with SFF. These materials, however, are usually quite weak, and suffer from many of the same problems described above.
Thus, there is still a need to provide novel build material compositions and methods for use in the solid free-form fabrication of three-dimensional objects.